Free piston pneumatic arrestor and control system



Nov. 7, 1967 E. K. MOORE, JR 3,3 0

FREE PISTON PNEUMATIC ARRESTOR AND CONTROL SYSTEM Filed Feb. 28, 1966 2 Sheets-Sheet 1 in: IIII ii fi \wwlll I N VE N TOR.

Y far/ KMaorey/r:

Liv Warez/5 L. Bel/51S NOV. 1967 E. K; MOORE, JR 3,351,021

FREE PISTON PNEUMATIC ARRESTOR AND CONTROL SYSTEM Filed Feb. 28, 1966 2 Sheets-Sheet 2 INVENTOR.

By gay/(WW6, J1;

44am; 1.. Bazes United States Patent Ofiice 3,351,021 Patented Nov. 7, 1967 3,351,021 FREE PISTON PNEUMATIC ARRESTOR AND CONTRUL SYSTEM Earl K. Moore, In, P1). Box 2486, Odessa, Tex. 79766 Filed Feb. 28, 1966, Ser. No. 530,514 14 Claims. (Cl. 10352) ABSTRACT OF THE DISCLOSURE A pneumatic means for controlling a well pumping apparatus of the free piston type, including a pneumatic cushion at the upper extremity of the tubing associated with the well. The penumatic cushion cooperates with the free piston in a manner to pneumatically decelerate the upward movement thereof of thereby prevent damage to the piston. The pneumatic cushion is connected to a shift piston assembly which actuates a flow control valve, which in turn controls the flow of fluid from the well. Upon striking the pneumatic cushion, the impact of the free piston against the pneumatic cushion provides a signal which is utilized by the shift piston to closethe flow valve. This action enables the free piston to drop to the bottom of the well. Upon the flow valve returning to the opened position, the free piston again travels upwardly through the well, and again strikes the pneumatic cushion, whereupon the flow valve is again return to the closed position.

The use of gas lifts in producing an oil well is a well known fluid recovery means and generally employs a free piston which is actuated by the pressure of the gas from the producing formation so as to cyclicly cause the piston within the tubing string to lift a slug of liquid from the oil bearing formation to a point of collection above the ground level. The free piston must accordingly reciprocate within the tubing string from one extremity thereof to the other. Generally, the pressure provided by the gas phase of the oil-gas mixture will build up in magnitude over a period of time, and at a predetermined time lapse, a motor valve control means located at the outlet end of the tubing string will be actuated, usually in response to a timer mechanism, and generally predicated upon the known history of the well, so as to open the motor valve which permits flow from the outlet end of the tubing string, thereby establishing a pressure differential across the plunger, and accordingly allowing the plunger to move upwardly through the tubing string thereby bringing with it a slug of liquid. When the plunger reaches the top of the tubing string the movement thereof is arrested and the motor valve closed. Soon thereafter the pressure across the plunger will equalize, and the plunger will fall by gravity to an abutment means located in the bottom of the eductor tube or tubing string, whereupon the plunger will then rest against the abutment means until the pressure has again built up to a suitable value whereupon the motor valve will again open and the cyclic process will start over again.

A primary problem which "has been recognized in conjunction with plunger lift apparatus is that the plunger in abutting the arresting apparatus located in the lubricator is subjected to a sudden deceleration. This deceleration, in the past art, is generally provided by a bumper pad and spring arrangement. Such an arrangement generally causes the spring to stack at a high rate, thereby causing the plunger to receive a severe shock each time it arrives into the lubricator. In a relatively short period of time this operation results in damage to the plunger and accordingly a malfunction in its performance.

It is a primary object of this invention to provide a pneumatic shock adsorber that will arrest the upward movement of the plunger as it enters the lubricator, to thereby provide a cushioned stop which accordingly results in a prolonged life of the plunger mechanism.

Another object of this invention is to provide a pneumatic sensing means that is triggered by the arrival of the plunger in the lubricator and in turn triggers a timing mechanism to there-by close the outflow motor valve which in turn allows the plunger to drop back to the bottom of the tubing string.

A still further object of this invention is to provide a novel combination pneumatic stop and penumatic sensing means that provides a control over the action of the plunger in addition to prolonging the life of the plunger.

A still further object of this invention is to provide a novel pneumatic control system in combination with a pneumatic sensing means and pneumatic arresting means.

The various features of novelty which characterize my invention is particularly pointed out in the claims that form a part of this specification. A complete understanding of this invention may be had from the following detailed description and the accompanying drawings referred to therein, illustrating the novel features by which the above objects set forth above are carried out.

In the drawings:

FIGURE 1 is a side elevational View, with some parts broken away, illustrating the preferred embodiment of the invention and showing the invention operatively associated with an oil well.

FIGURE 2 is a cross sectional view on an enlarged scale, showing the details of part of the invention illustrated in FIGURE 1.

FIGURE 3 is a cross sectional view of a portion of the controller mechanism seen in FIGURE 1.

FIGURE 4 is an elevational view of an enlarged detail of part of the device of FIGURE 1.

FIGURE 5 is an enlarged cross sectional view taken along lines 5-5 of FIGURE 4.

FIGURE 6' is an enlarged cross sectional view taken a ong lines 66 of FIGURE 4.

Referring now to the drawings in greater detail, the invention as illustrated therein is operatively associated with a hydrocarbon producing formation. As illustrated in FIGURE 1 there is shown a tubing string 20 positioned mostly within a well casing 18 having a cap 19 in sealing relationship with the tubing string 20 and casing 18. The lower extremity of the tubing string is provided with a stop means or retainer means in the form of a lower bumper pad through which liquid petroleum products from the oil producing formation flows, and which also acts as an abutment means for the traveling plunger 200. Located above the casing and operatively associated with the tubing string is a plunger retainer means 24 which provides a means by which the plunger can be retained Within the lubricator. The details of the upper plunger retainer means 24 are well known in the art. Above the plunger retainer is a coupling 26 having an outflow pipe 28 perpendicular thereto and a shock adsorber body 34 upstanding therefrom. A motor valve 38 having a valve body 30 is series connected in line 28 and operatively connected to outlet 32 which usually leads to a tank battery, sales gas line, or other collection means. The motor valve 38 is operatively associated with timer mechanism 40 and includes the various pneumatic circuitry necessary for a timed cycle operation of the normally closed motor valve 38 as will be explained more fully later on.

The shock adsorber body 34 has a cap 36 removably secured thereto and is suitably apertured to receive a valve 70 at the upper extremity of the cap. The body 34 together with the cap 36 may alternatively be cast as an integral part, if desired. The body 34 may be provided with various reducers and the like to enable attachment to any existing gas lift device.

Looking now to the details of FIGURE 2 wherein there is disclosed the novel pneumatic plunger arrester. The body 34 is removably connected by suitable threaded connections to coupling 26 and has located therein an O-ring 51 in sealing relationship between the body and the coupling. Handles 42 are welded to the body 34 to provide a means by which the body may be readily removed from the remaining portion of the lubricator. The shock adsorber body is preferably provided with grooves 44 that extend a sufiicient distance along the body so as to connect the chamber 35 of upper body portion 34 with the lower body portion below bumper 50 located within body 34 when the bumper pad is located at its lowest points of travel so as to thereby enable any accumulative fluid and foreign material to drain from the shock adsorber body back into the remaining portion of the lubricator. Grooves are located circumferentially about the outer periphery of the bumper pad 50 and receive Teflon rings 52, 52, 52" therein in sealing relationship between the bumper pad and the inner cylindrical surface of the shock adsorber body. The bumper pad 50 is further provided with a passageway 54 leading to a valve seat 64 at the bottom of enlarged chamber 58. A removable orifice 56 is suitably threaded into chamber 58 and a ball check valve 62 is carried therewithin. A spring 66 is suitably provided as illustrated in the shock adsorber body, and is of a length shorter than the free displaced length of the shock adsorber body, and is adapted to be compressed between the upper face of pad 50 and chamfered area 69.

A shock adsorber cap 36 threadedly engages the shock adsorber body 34 as illustrated at 68. The before mentioned charnfered edge illustrated at numeral 69 forms an abutment for the upper extremity of spring 66 in order to maintain the bumper pad within the cylindrical portion of body 34. The inside diameter of the cap is reduced at outlet 72 and receives a needle valve 70 therein that is adapted to control the rate of response of a shift piston assembly 80 with respect to the pressure impulse generated by the bumper pad as it is upset by the plunger.

A shift piston assembly is indicated generally in FIG- URE 3 by the numeral 80 and is comprised of a piston 90 that is slidably located within a cylindrical chamber 96 formed by the shift piston rear housing 92 and the shift piston front housing 94 which are threadedly mated together in sealing relationship as indicated at 93. The shift piston assembly has a front outlet 82 and a rear outlet 84 adapted to be connected to conduits 83, 85 respectively which in turn are connected to the needle valve 70 and to the connection 46 located in the coupling 26 respectively. A feeler finger 86 is suitably attached, as by a set screw or the like as indicated, to a feeler finger shaft 88 which in turn is slidably received in a shaft aperture 95 and provided with suitable packing 97 as is well known in the art. The feeler finger shaft is threadedly engaged at 98 to piston 90.

Looking now to the details of the intermitter pilot 105 that is operatively associated with the before described shift piston assembly 80, there is seen in FIGURES 4, 5, and 6 the intermitter pilot body 132 that may be similar to type 4500 or 4501, manufactured by the Fisher Groverner Company of Marshaltown, Iowa, USA. The intermitter pilot is provided with a regulated pilot pressure source at 134, a pressure fitting 135 adapted to be connected to the motor valve 38, and includes a pilot control valve assembly 136, the details of which is well understood in the art, and a spring biased flapper lever 140 associated with the pilot nozzle or control valve assembly outlet 138. The spring portion 144 of the flapper is secured to the body 132 by screws 142. When the flapper 140 is urged away from the outlet 138 the regulated pilot pressure source 134 is transmitted through fitting 135 to the motor valve 38 to accordingly lift the valve within the housing 30 from its seat so as to provide for the before mentioned fluid flow through outlet pipe 28. When the flapper 140 is released so as to abut the pilot nozzle 138, the pneumatic signal to motor valve 38 is reduced in intensity thereby permitting the normally closed valve 38 to return to the closed position. The intermittent pilot assembly is modified in a novel manner by providing an inflexible trigger 118 pivotally mounted by pivot screw that includes a spring biased means 146 that urges the trigger 118 in a counterclockwise rotational direction until it either abuts a suitable stop means or comes to rest in a position whereby the contoured end near the numeral 118 will ride on the outer periphery 102 of the rotatable disk 41. As rotatable disk 41 rotates in a counterclockwise direction, a trigger cam 104 of the timing wheel will rotate the inflexible trigger portion 118 about the pivot screw 120 so as to cause the trigger to be rotated a limited amount in a clockwise direction for a predetermined length of time and in a predetermined cycle of operation. Rigidly attached at one extremity of the inflexible trigger portion 118 is a flexible portion 116 of the trigger that is adapted to be sprung away from the inflexible trigger portion 118 as illustrated in FIGURES 5 and 6. The flexible member 116 is attached to the inflexible trigger portion 188, as by screw 122, and is provided with a depending edge portion that is adapted to engage the end 124 of flapper 140. A rod 126, is journaled in bushing 128 to the adjustment plate 106 of of the intermittent pilot assembly and is adapted to engage the flexible member 116 of the trigger assembly as illustrated in FIGURES 4 and 5. The rod end 126 is adapted to flex member 116 away from the remaining trigger assembly so as to permit flapper to move into engagement with nozzle 138 of the pilot valve assembly. The rod end 130 is looped about the feeler finger shaft 88 and engages the feeler finger 86 upon actuation by the shift piston assembly 80.

FIGURE 4 shows the end 124 of flapper 140 engaged with the flexible member 116 of the trigger assembly. Upon actuation of the shift piston assembly 80, shift piston 90 moves in a direction so as to shorten the effective length of shaft 88 which in turn causes the feeler finger 86 to engage the loop at 131 of the rod portion 130, whereupon the rod 130 rotates in its bushing 128 and accordingly engages flexible member 116 of the trigger assembly thereby permitting end 124 of flapper 140 to be released from engagement with the edge of member 116 and spring into the position shown in FIGURE 6 whereby the flapper 140 will then engage the pilot control valve nozzle 138 as illustrated in FIGURES 5 and 6.

After the shift piston assembly has triggered the pilot, as in the above described manner, further rotation of the rotatable disk 41 will allow the inflexible trigger portion 118 to ride off the trigger cam of the wheel whereupon the spring bias means 146 will permit rotation of the trigger assembly in a counterclockwise direction about pin 120 as the contoured end of the trigger rides off the trigger cam 104 onto the outer periphery 102 of the wheel, thereby allowing the flexible portion 116 of the trigger assembly to move in a counterclockwise direction to clear end 124 of flapper 140. Hence it may be seen that flexible trigger member 116 actuates end 124 of flapper valve 140 as the inflexible trigger portion 118 rides on the irregular periphery of the rotatable disk 41. As the trigger assembly rides the irregular portion of the rotatable disk, flapper valve 140 is accordingly seated and unseated from nozzle 138 that controls the pilot valve 132 that in turn controls the motor valve 38. It will now be clear to those skilled in the art that flexible member 116 of the trigger assembly provides a means by which each normal cycle of the timing means may be interrupted by the shift piston assembly 80 by the shift piston feeler finger 86 moving the lever comprised of rod 126, 130 that in turn permits the flapper 140 to be seated against nozzle 138. Since the shift piston assembly 80 is actuated by the pneumatic impulse caused by the free piston 200 abutting the bumper pad 50, the free piston 200 may be said to interrupt the normal timed cycle of motor valve 38 in accordance with the position of the free piston or plunger 200.

It should be noted that while the shift piston assembly causes movement of the lever comprised of rod 126, 130 against flexible :member 116 of the trigger assembly, that the rod end 126- is not directly attached to flexible member 116. Hence, should it be desirable to remove the shift piston assembly from service, as by closing valve 70, on the pneumatic shock adsorber body 34, the timed cycle of the gas lift would continue in accordance to the mechanical configuration of the trigger cams 104 on the rotatable disk 41. Furthermore, the shock adsorber 34 would still function as a novel pneumatic means of decelerating the free piston at the upper extremity of its travel.

In operation, the timing mechanism 40 is set to actuate the motor valve 38 from open to closed position at a predetermined interval of time in accordance with the known history of the well conditions. The rotatable disk 41 is provided with a number of cams 104 spaced at suitable intervals about the outer periphery 102 thereof, so as to actuate the pilot valve assembly 105- at predetermined intervals. The pilot valve has a throttling mechanism comprised of a flapper valve, as is well konwn in the art, that when opened sends a pressure signal to the bottom of a diaphragm located in the motor valve 38, thereby causing the normally closed valve in valve housing 30 to open. Absence of this pressure signal permits the spring loaded normally closed valve in housing 30 to return to the closed position. At the beginning of a timed cycle, the plunger 200 will be resting on the bottom of the bore hole against the lower bumper pad, and the rotatable disk 41 of timer 40 will rotate in a direction to move the flapper valve of the pilot assembly 105 that in turn sends a pneumatic signal to the chamber below the diaphragm of motor valve 38 thereby opening the valve within the housing 30'. Upon the valve within housing 30 opening, the pressure differential across the plunger will cause the plunger to move upwardly with the column or slug of fluid in the tubing above the plunger accordingly being forced upward through the tubing string 29 into'coupling 26, Where it will then flow through outflow pipe 28, valve body 30, and outlet pipe 32 to the gathering system. When the free plunger 200 reaches the lubricator, the top of the plunger will abut the bumper pad 50 with sufiicient inertia that during the pneumatic deceleration of the free plunger, the bumper pad will be forced upwardly into the chamber 35 of the shock adsorber body 34 and accordingly compress the fluid contained therein. The fluid contained in chamber 35 is, of course, the same gaseous fluid associated with the liquid hydrocarbon flowing through the tubing string. In the case where the plunger 209 has sufficient inertia to force the bumper pad abnormally further towards the top of the shock adsorber body 34, the spring 66 will abut the chamfered edge 69 of the cap 36 and this compressive force of spring 66 in conjunction with the compression of the fluid within chamber 35 will provide a cushioned stop to thereby arrest movement of the plunger 200. All this time the controller 40 is still holding the motor valve 38 in an open position. The sudden compression of the fluid within chamber 35 is transmitted by conduit 83 to the shift piston assembly 80 where the signal is imposed below the shift piston 90, thereby retracting the feeler finger shaft 88 and causing the flapper valve on the pilot to be released by the flexible member 116 whereby the pressure on the under side of the motor valve 38 is then reduced thereby closing the valve within motor valve housing 30. Closure of the motor valve 138 permits the pressure to equalize on each side of the plunger, and the plunger accordingly drops back down through the tubing string by gravity until it again engages and rests on the lower bumper pad at the bottom of the string.

After the plunger has begun to fall by gravity back into the tubing, the bumper pad Will. return to its original position. The weight of the bumper pad in conjunction with the one-way ball check valve 62 permits equalization of the pressure on either side of the bumper pad so as to permit the return of the pad to its original position. The bottommost portion of the shock adsorber body is provided with the before mentioned grooves 44 milled longitudinally into the side thereof and of a length slightly longer than the thickness of the bumper pad, to thereby permit any entrapped liquid that may collect in chamber 35 to accordingly drain. therethrough and back into the lubricator.

Upon the plunger 22 reaching the lower bumper pad at the lower extremity of the tubing string, the plunger will remain in the bottom of the hole until the expiration of a predetermined time period whereupon the timer 44) again opens the motor valve in the valve housing 30, thereby allowing another cycle of operation to begin.

It should be understood that the shock adsorber body and bumper pad arrangement can be used in a gas lift either alone so as to take advantage of the present novel arresting means, or in conjunction with the instant novel pneumatic control associated with the travel of the free plunger. Hence the upper section comprising the shock adsorber body and bumper pad assembly has the dual purpose of providing an arresting means for a free plunger while at the same time providing a novel pneumatic control means wherein the timed interval of the free plunger is controlled pneumatically.

In the instant novel device, the lubricator 19 is shown as having a single motor valve controlled outlet 32, hence in the arrangement depicted by the drawings, the application of the novel device as illustrated would be associated with a hydrocarbon formation wherein the free piston 20f) would cycle the liquid in a manner to provide the major flow means for the fluid from the hydrocarbon formation. The instant novel device may also be used in applications where the free piston 200 is cycled occasionally so as to remove paraflin or gyp from the tubing string, for lowering gas-oil ratios, to extend the flowing life of a free flowing well, to increase efliciency on gas lift, for unloading gas wells, and to minimize emulsion. In the application where the instant novel device is employed to unload gas wells, a second flow line may advantageously be connected at coupling 26 and a check valve placed therein so as to enable outlet 32 to flow to a low pressure system and the timer 40 accordingly set so as to unload the gas well in a predetermined cycle of operation designed to avoid the buildup of a fluid head within the tubing string 20.

While I have shown a practical and eflicient embodiment of the features of my invention, I do not desire to be limited to the exact construction and arrangement shown and described, as changes are possible without departing from the scope of this novel invention.

I claim as new and desire to secure by Letters Patent:

1. A well pumping apparatus comprising a well tubing having an inlet and an outlet above the inlet;

a flow valve for controlling the flow of fluid through said outlet;

a free piston in said tubing;

first means for periodically opening and closing said pneumatic shock adsorber means located above said outlet and positioned with respect to said tubing so as to pneumatically decelerate said piston;

and second means responsive to said pneumatic shock adsorber means and adapted to cooperate with said first means to cause the valve to close upon said free piston engaging and being decelerated by said pneumatic shock adsorber means.

2. The well pumping apparatus of claim 1, wherein said pneumatic shock adsorber means includes a chamber having a movable wall therein; whereby, said free piston upon striking said movable wall compresses fluid therein and decelerates said piston.

3. The well pumping apparatus of claim 2, wherein said second means includes a shift piston;

said shift piston including a chamber having a movable wall therein, and means connecting the last said chamber to said chamber of said shock adsorber means whereby compression of fluid within the last named chamber moves said movable wall in said shift piston; and

said second means is associated with said movable wall of said shift piston; whereby,

impact of the free piston against said movable wall of said pneumatic shock adsorber means compresses fluid contained therein to thereby move said movable wall associated with said shift piston to thereby cause said first means to be actuated and thereby stop the flow of fluid from the well.

4. The device of claim 1 wherein said pneumatic shock adsorber means includes a cylinder having one end rigidly and concentrically attached to said tubing and a free end depending therefrom;

a closure means on said free end;

a bumper pad slidingly and sealingly received within said cylinder whereby said pad may be urged upwardly towards said closure means by said piston and be urged downwardly by gravity;

said second means including pneumatic responsive means connected to sense the pneumatic pressure in said shock adsorber means and connected to actuate said flow valve from the open to the closed position upon an increase in pressure in said shock adsorber.

5. The device of claim 1 wherein said second means includes a shift piston assembly comprising a housing forming a chamber therein, a piston slidably received in sealed relationship within said housing and having a feeler rod extending from said housing and connected to said shift piston;

the end of said rod engaging said first means for causing said flow valve to close upon said pneumatic shock adsorber means being engaged by said free piston.

6. The device of claim 5 wherein said first means includes an intermittent flapper controlled pilot valve operatively associated with a pneumatically actuated motor for said flow valve;

said flapper controlled pilot valve opens said motor valve when said pilot valve is open and closes said motor valve when said pilot valve is closed by said flapper;

lever means associated with said flapper and said feeler rod to actuate said flapper to the open position upon said pneumatic shock adsorber means being engaged by said free piston.

7. In a lubricator associated with a gas lift well, a shock adsorber for decelerating the upward travel of a free piston comprising:

a chamber positioned concentrically about and rigidl attached to the lubricator of the well with a free end of said chamber depending upwardly from the lubricator;

a closure member on said free end;

a shock piston slidably received in sealed relationship within said chamber;

one-way check valve means associated with said chamber for preventing gas flowing therethrough during compression thereof and for permitting gas to enter said chamber after said shock piston has reached the upper limit of its travel, whereby;

impact of the free piston against the shock piston will pneumatically decelerate the free piston, and said shock piston will thereafter return to its original position by gravity.

8. The device of claim 7, and further including a shift piston assembly for controlling a pneumatically operated motor valve in response to a pressure signal from said chamber;

said shift piston assembly including a sealed chamber having a movable member therein dividing said chamber into a first and second chamber;

said first and second chambers having means for producing a pressure differential therebetween in response to a pressure signal from said chamber;

a finger rod attached to said movable member and extending away from said sealed chamber for effecting movement of said rod in accordance with the position of said movable member;

a pneumatically controlled intermittent pilot valve operatively associated with a pneumatically operated motor valve;

said intermittent pilot valve having means including a resilient flapper covering a nozzle for causing said pilot valve to open said motor valve when said nozzle is uncovered and for closing said motor valve when said nozzle is covered by said flapper;

said flapper associated with lever means to normally actuate said flapper from the opened to the closed position with respect to said nozzle and in a timed cycle of operation;

a resilient member associated with said lever means for contacting said flapper;

said finger rod having an end thereof adjacent said lever means and adapted to urge said resilient member out of contact with said flapper upon said shift piston receiving a pressure signal.

9. A pneumatically responsive shift piston assembly for controlling a pneumatically operated motor valve in response to a pressure signal, comprising:

a sealed chamber having a movable member therein dividing said chamber into a first and second chamber;

said first and second chambers having means for producing a pressure differential therebetween in response to a pressure signal;

a finger rod attached to said movable member and extending away from said chamber for movement in accordance with the position of said movable member;

a pneumatically controlled intermittent pilot valve operatively associated with a pneumatically operated motor valve;

said intermittent pilot valve including a nozzle and resilient flapper with said resilient flapper covering said nozzle for causing said pilot valve to open said motor valve when said nozzle is uncovered and for closing said motor valve when said nozzle is covered by said flapper;

said flapper associated with lever means to normally actuate it from the opened to the closed position with respect to said nozzle and in a timed cycle of operation;

a resilient member associated with said lever means for contacting said flapper;

said finger rod having a portion thereof adjacent said resilient member and adapted to urge said resilient member out of contact with said flapper upon said shift piston receiving a pressure signal to thereby close said nozzle which in turn actuates the motor valve to the closed position.

10. In a well pumping apparatus including a well tubing having an inlet, an outlet above the inlet, a flow valve for controlling the flow of fluid through the outlet, and a free piston, in the tubing for raising liquid from the inlet to the outlet, the improvement comprising:

first aineans for periodically opening and closing the flow v ve;

pneumatic shock adsorber means located above the outlet and positioned with respect to the tubing so as to pneumatically decelerate the free piston; and

second means for causing the flow valve to close in response to the free piston being decelerated by said pneumatic shock adbsorber means.

11. The apparatus of claim 10, wherein said pneumatic shock adsorber means includes a chamber adapted to contain a fluid therein and having a movable wall therein; whereby, the free piston upon striking said movable wall compresses fluid therein and decelerates the piston.

12. The apparatus of claim 10, wherein said pneumatic shock adsorber means includes a chamber having one end rigidly and concentrically attached to the tubing and a free end depending therefrom;

a closure means on said free end;

a bumper pad means slidingly and sealingly received within said chamber whereby said pad may be urged upwardly towards said closure means by the free piston and be urged downwardly by gravity;

said second means including pneumatic responsive means connected to sense the pneumatic pressure in said chamber and connected to actuate said first means to thereby change the flow valve from the open to the closed position upon an increase in pressure in said chamber.

13. The apparatus of claim 12 wherein said pneumatic responsive means includes a shift piston assembly comprising a housing forming a chamber therein, a piston slidably received in sealed relationship within said housing and having a feeler rod extending from said housing and connected to the last said piston;

a portion of said rod engaging said first means for causing the flow valve to close upon said bumper pad being engaged by the free piston.

14. The apparatus of claim 13 wherein said first means for causing the flow valve to close includes an intermittent pilot valve operatively associated with a pneumatically actuated motor for the flow valve;

said first means including a flapper controlled pilot valve that opens the motor valve when said pilot valve is open and closes the motor valve when said pilot valve is closed by said flapper;

lever means associated with said flapper and said feeler rod to actuate said flapper to the open position upon said bumper pad being engaged by the free piston.

References Cited UNITED STATES PATENTS 2,508,174 5/1950 Knox et al. 103-52 2,674,951 4/1954 Zaba 103-52 2,766,694 10/1956 Vincent 103-62 2,940,477 6/1960 Brown et a1. 3,304,874 2/1967 Lyles 10352 ROBERT M. WALKER, Primary Examiner. 

1. A WELL PUMPING APPARATUS COMPRISING A WELL TUBING HAVING AN INLET AND AN OUTLET ABOVE THE INLET; A FLOW VALVE FOR CONTROLLING THE FLOW OF FLUID THROUGH SAID OUTLET; A FREE PISTON IN SAID TUBING; FIRST MEANS FOR PERIODICALLY OPENING AND CLOSING SAID FLOW VALVE; PNEYMATIC SHOCK ADSORBER MEANS LOCATED ABOVE SAID OUTLET AND POSITIONED WITH RESPECT TO SAID TUBING SO AS TO PNEUMATICALLY DECELERATE SAID PISTON; AND SECOND MEANS RESPONSIVE TO SAID PNEUMATIC SHOCK ADSORBER MEANS AND ADAPTED TO COOPERATE WITH SAID FIRST MEANS TO CAUSE THE VALVE TO CLOSE UPON SAID FREE PISTON ENGAGING AND BEING DECELERATED BY SAID PNEUMATIC SHOCK ADSORBER MEANS. 